Original Article
Predictors of Event-Free Survival after Balloon Aortic Valvuloplasty
N Engl J Med 1991; 325:17-23July 4, 1991
- Abstract
- Abstract
Background.
Balloon aortic valvuloplasty was developed as an alternative to aortic-valve replacement in selected elderly patients with aortic stenosis. The use of this procedure is limited, however, by a high incidence of re-Stenosis.
Methods.
Between December 1985 and April 1989, valvuloplasty was performed in 205 patients. We evaluated 40 demographic and hemodynamic variables as univariate predictors of event-free survival by Cox regression analysis and identified independent predictors of eventfree survival by stepwise multivariate analysis.
Results.
Early hemodynamic results indicated a decrease in the peak transaortic-valve pressure gradient from 67±28 to 33±15 mm Hg after valvuloplasty and an increase in aortic-valve area from 0.6±0.2 to 0.9±0.3 cm2 (P<0.001 for both comparisons). The rate of event-free survival (defined as survival without recurrent symptoms, repeated valvuloplasty, or aortic-valve replacement) was 18 percent over the mean (±SD) follow-up period of 24±12 months (range, 1 to 47). Significant predictors of event-free survival included the left ventricular ejection fraction and the left ventricular and aortic systolic pressure before valvuloplasty, and the percent reduction in the aortic-valve pressure gradient; the pulmonary-capillary wedge pressure was inversely associated with event-free survival. Although the predicted event-free survival rate for the entire patient group was 50 percent at one year (95 percent confidence interval, 43 to 57 percent) and 25 percent at two years (95 percent confidence interval, 19 to 31 percent), the probability of event-free survival at one year varied between 23 and 65 percent when patients were stratified according to three independent predictors: the aortic systolic pressure, the pulmonary-capillary wedge pressure, and the percent reduction in the peak aortic-valve gradient.
Conclusions.
The most important predictors of event-free survival after balloon aortic valvuloplasty were related to base-line left ventricular performance. The best long-term results after valvuloplasty were observed among patients who would also have been expected to have excellent long-term results after aortic-valve replacement. (N Engl J Med 1991; 325:17–23.)
Media in This Article
Figure 1
Actuarial Total and Event-free Survival among 205 Patients Treated by Balloon Aortic Valvuloplasty (BAV).Table 1
Base-Line Characteristics of Patients Undergoing Balloon Aortic Valvuloplasty.Article Activity
- Article
BALLOON aortic valvuloplasty was initially developed as an alternative to aortic-valve replacement for elderly patients with symptomatic aortic stenosis for whom the risks of aortic-valve replacement were felt to be high.1 , 2 Early reports documented the safety and immediate hemodynamic effects of balloon dilation.3 4 5 Follow-up studies demonstrated, however, that long-term hemodynamic improvement was limited by a high incidence of re-Stenosis, which approached 50 percent within one year of the procedure.6 7 8 9 Furthermore, recent reports have suggested that aortic-valve replacement may be a reasonable treatment for selected octogenarians with symptomatic aortic stenosis; among such patients perioperative mortality has been found to be less than 10 percent.10 11 12 13 14 15 The purpose of our study was to identify clinical and procedure-related predictors of event-free survival after balloon aortic valvuloplasty.
Methods
Study Population
Between December 1985 and April 1989, we performed balloon aortic valvuloplasty in 205 patients with symptomatic aortic stenosis. The characteristics of the first 170 patients were described previously6; those of the entire group are shown in Table 1Table 1
Base-Line Characteristics of Patients Undergoing Balloon Aortic Valvuloplasty.. The indications for the procedure remained constant during the study period. Valvuloplasty was performed either in patients who were not considered to be candidates for surgery or in patients who refused surgery.Aortic-Valvuloplasty Procedure
The technique of balloon aortic valvuloplasty has been described elsewhere.2 , 6 Informed consent was obtained in accordance with a protocol approved by the Committee for Clinical Investigations of Beth Israel Hospital. Balloon dilation was performed with balloons ranging from 12 to 25 mm in diameter (Boston Scientific, Waltham, Mass., and Cook, Bloomington, Ind.) until a 50 percent reduction in the transaortic-valve pressure gradient was achieved, if possible. Hemodynamic values and Fick cardiac output were determined before and immediately after valvuloplasty. Six patients underwent simultaneous balloon mitral valvuloplasty, and 12 patients underwent simultaneous coronary angioplasty, as described elsewhere.16 , 17
Clinical Follow-up
Follow-up information was obtained at intervals of 3, 6, and 12 months after valvuloplasty and at 6-month intervals thereafter during patients' visits to the clinic or by telephone contact with the patient, his or her referring physician, or both. A second cardiac catheterization was recommended for all patients with recurrent symptoms. re-Stenosis was defined as loss of 50 percent of the initial increase in aortic-valve area. For purposes of analysis of event-free survival, late events were defined as recurrent symptoms, repeated valvuloplasty, aortic-valve replacement, or death (death was from cardiac causes in all but one patient who died).
Statistical Analysis
Hemodynamic measurements before and after valvuloplasty were compared with use of paired t-tests, and data are reported as means ±SD. Kaplan–Meier estimates were used to determine total and event-free survival. Forty demographic and hemodynamic variables were evaluated by Cox regression analysis as possible continuous univariate predictors of event-free survival. A similar analysis was performed with data on a subgroup of patients over 80 years of age. Significant continuous univariate predictors were chosen for univariate analysis; clinically reasonable cutoff points were used to construct categorical variables for comparison with the log-rank statistic. Unadjusted relative-hazard ratios were calculated for each variable (relative risk), and Kaplan–Meier probabilities of event-free survival were estimated for each variable at 6, 12, 18, and 24 months after valvuloplasty.
All variables identified as significant predictors in the univariate analysis were considered in a Cox proportional-hazards regression analysis. By stepwise multivariate analysis, independent predictors of event-free survival were identified. The Cox proportional-hazards model was then used to estimate the probability of event-free survival at 6, 12, 18, and 24 months on the basis of a two-variable model and a three-variable model.
Results
Base-Line Characteristics of the Patients
Balloon aortic valvuloplasty was performed in 205 patients (mean age, 78±10 years) with symptomatic aortic stenosis; of these, 82 percent had congestive heart failure, 36 percent had angina, and 25 percent had syncope (Table 1). We were unable to classify the patients according to functional impairment by the New York Heart Association classification system, since it was extremely difficult to identify the four symptom classes in elderly patients with limited physical capacity.
Immediate Hemodynamic Results
Balloon aortic valvuloplasty was completed successfully in 203 of the 205 patients (99 percent) and resulted in a decrease in the mean transaortic-valve pressure gradient from 55±19 to 30±12 mm Hg, a decrease in the peak transaortic-valve pressure gradient from 67±28 to 33±15 mm Hg, and an increase in cardiac output from 4.4±1.4 to 4.8±1.4 liters per minute (P<0.001 for all comparisons). The calculated aortic-valve area increased from 0.6±0.2 to 0.9±0.3 cm2 (P<0.001). There were immediate decreases in the peak left ventricular systolic pressure (from 195±35 to 171±27 mm Hg), in the mean pulmonary-capillary wedge pressure (from 20±8 to 17±8 mm Hg), and in the mean pulmonary-artery pressure (from 30±11 to 27±10 mm Hg; P<0.001 for all comparisons). The arterial systolic pressure increased from 127±25 to 138±25 mm Hg (P<0.001), and there was no significant change in arterial diastolic pressure (58±11 to 59±12 mm Hg). Immediate results and early follow-up results for the first 170 patients have been reported previously.6
In-Hospital Course
Balloon aortic valvuloplasty was completed successfully in 203 patients and was aborted in 2 patients as a result of perforation of the left ventricle by the guide wire in one patient and iliac-artery perforation in another, as reported previously.6 The incidence of all complications is shown in Table 2Table 2
In-Hospital Complications of Balloon Aortic Valvuloplasty.. Among the remaining 203 patients, there were 9 early deaths (Table 2), and 6 patients required early valve replacement (including 1 of the 9 who died during hospitalization) because of the poor hemodynamic results of valvuloplasty and concomitant severe coronary artery disease.Clinical Follow-up
Follow-up data for a period averaging 24 months (range, 1 to 47) were available for all 189 patients discharged from the hospital after successful valvuloplasty without subsequent aortic-valve replacement. Recurrent symptoms developed in 155 patients (82 percent) and led to medical therapy in 5 patients (3 percent), repeat valvuloplasty in 42 patients (22 percent), aortic-valve replacement in 51 patients (27 percent), and death in 57 patients (30 percent). At the last follow-up contact, 76 patients (40 percent) had died a mean of 13±9 months after discharge from the hospital; the most common cause of death was progressive congestive heart failure.
The total survival rate was 75 percent at one year and 60 percent at two years. In contrast, the probability of event-free survival at one year was only 50 percent (95 percent confidence interval, 43 to 57 percent) and 25 percent at two years (95 percent confidence interval, 19 to 31 percent) (Fig. 1Figure 1
Actuarial Total and Event-free Survival among 205 Patients Treated by Balloon Aortic Valvuloplasty (BAV).).Univariate Analyses
We analyzed as possible predictors of long-term event-free survival demographic characteristics, hemodynamic values before valvuloplasty, hemodynamic values after valvuloplasty, changes in hemodynamic values, and balloon size (Table 3Table 3
Categorical Predictors of Event-free Survival, According to Univariate Analysis, in 205 Patients Undergoing Balloon Aortic Valvuloplasty.*). Analyses were conducted for the entire group of patients (n = 205) and for the subgroup of patients 80 years of age or older (n = 110).Female sex was the only demographic variable that was associated with long-term event-free survival, whereas age, the presence of sinus rhythm, and the extent of coronary artery disease were not. Direct predictors of long-term event-free survival included the left ventricular ejection fraction, left ventricular systolic pressure, and aortic systolic pressure. Inverse predictors of event-free survival included the pulmonary-capillary wedge pressure and pulmonary-artery pressure. Whereas the cardiac index before valvuloplasty was directly associated with outcome and the right atrial pressure before the procedure was inversely associated with outcome, the cardiac index and right atrial pressure after valvuloplasty were not important predictors of long-term outcome.
The base-line aortic-valve area and aortic-valve gradient (before valvuloplasty) and the final aortic-valve area and aortic-valve gradient (after valvuloplasty) were not associated with event-free survival. However, the percent reduction in the peak aortic-valve gradient was a strong predictor of long-term event-free survival. For patients with a left ventricular ejection fraction of less than 40 percent, improvement in the ejection fraction was directly associated with event-free survival.
When patients 80 years of age or older were analyzed as a subgroup, univariate analysis indicated that the predictors of long-term event-free survival were the same in this subgroup as in the entire group of patients. We have therefore reported only the stratified univariate analyses (Table 3) and multivariate analyses (Tables 4Table 4
Independent Predictors of Event-free Survival, According to Multivariate Cox Proportional-Hazards Regression Analysis, in 205 Patients Undergoing Balloon Aortic Valvuloplasty.*, 5Table 5
Estimated Event-free Survival According to Base-Line Hemodynamic Variables.*, and 6Table 6
Estimated Event-free Survival According to Base-Line Hemodynamic Variables, with Stratification According to the Reduction in the Peak Aortic-Valve Gradient.*) for the entire group.Multivariate Analysis
In the stepwise multivariate analysis (Table 4), the only independent predictors of event-free survival were the base-line aortic systolic pressure, the base-line pulmonary-capillary wedge pressure, and the percent reduction in the peak aortic-valve gradient. A base-line aortic systolic pressure <110 mm Hg was associated with a relative risk of late events of 2.03 (95 percent confidence interval, 1.33 to 3.08), and a base-line pulmonary-capillary wedge pressure >25 mm Hg was associated with a relative risk of 1.73 (95 percent confidence interval, 1.18 to 2.55), as compared with the risk in patients with a base-line aortic systolic pressure ≥140 mm Hg and a pulmonary-capillary wedge pressure <18 mm Hg, respectively (Table 4). In addition, a reduction of less than 40 percent in the peak aortic-valve gradient was associated with a relative risk of late events of 1.75 (95 percent confidence interval, 1.17 to 2.63), as compared with the risk in patients in whom valvuloplasty resulted in a reduction of 55 percent or more in the peak aortic-valve gradient.
Using the two independent base-line hemodynamic variables from the Cox model, we estimated the probability of event-free survival at 6, 12, 18, and 24 months for all patients (Table 5). According to this two-variable predictive model, patients with base-line pulmonary-capillary wedge pressure <18 mm Hg and aortic systolic pressure ≥140 mm Hg had event-free survival rates of 65 percent at one year and 41 percent at two years. In contrast, patients with base-line pulmonary-capillary wedge pressure >25 mm Hg and aortic systolic pressure <110 mm Hg had event-free survival rates of only 23 percent at one year and 4 percent at two years.
When the data were further stratified according to the percent reduction in the peak aortic-valve gradient, additional estimates of event-free survival were possible (Table 6). However, this model may be less useful than the two-variable model for decision making, since it relies on data obtained after the completion of the valvuloplasty procedure.
Discussion
Prognosis of Patients with Untreated Aortic Stenosis
Early studies of the natural history of symptomatic aortic stenosis suggested a five-year survival rate of 48 percent for younger patients with primarily rheumatic aortic stenosis.18 , 19 However, degenerative calcification of a bicuspid or tricuspid aortic valve is now the most common cause of aortic stenosis in the United States,20 and the prognosis for elderly patients with untreated symptomatic stenosis is poor, with a one-year survival rate of 57 to 60 percent and a two-year survival rate of 37 to 40 percent.21 , 22 In contrast, elderly patients without aortic stenosis have a one-year survival rate of 93 percent and a two-year survival rate of 85 percent.21
The Role of Aortic-Valve Replacement
Aortic-valve replacement is the standard treatment for most patients with aortic stenosis and is associated with perioperative mortality rates of 1 to 3 percent. The long-term benefits of aortic-valve replacement are well established and include marked hemodynamic improvement, regression of left ventricular hypertrophy, enhanced left ventricular performance, and increased survival.23 , 24 , 25 However, perioperative mortality rates are higher among patients with clinically important left ventricular dysfunction and severe coronary artery disease. The need for emergency surgery is the most important risk factor and is associated with perioperative mortality rates of 25 to 40 percent or higher.10
There is considerable controversy about whether advanced age is an important risk factor for cardiac surgery.10 , 13 , 14 , 26 , 27 Edmunds and coworkers reported a 33 percent perioperative mortality rate among octogenarians who underwent isolated aortic-valve replacement.11 In contrast, other investigators have reported perioperative mortality rates of 6 to 13 percent among patients in their 70s and 80s12 13 14 15; two recent studies reported perioperative mortality rates of less than 10 percent among elderly patients undergoing aortic-valve replacement.12 , 13 Furthermore, one study found one-year and five-year survival rates of 83 percent and 67 percent, respectively — rates that are similar to the actuarial survival of age-matched controls without aortic stenosis12 (Fig. 1).
Predictors of Event-free Survival after Balloon Aortic Valvuloplasty
In the univariate analysis, the most important predictors of event-free survival after valvuloplasty were hemodynamic factors associated with preserved left ventricular function. Predictors of event-free survival among patients 80 years of age or older were identical to those for the entire group. Patients with a base-line left ventricular ejection fraction of less than 25 percent had a relative risk of a late event that was 2.6 times higher than that among patients with a base-line ejection fraction ≥60 percent. Furthermore, the unadjusted rates of event-free survival at one year were 28 percent and 65 percent, respectively, for these two subgroups. In addition, elevated pulmonary-capillary wedge pressure was associated with reduced event-free survival after valvuloplasty, independent of left ventricular systolic performance. Base-line left ventricular performance has also been shown by others to be an important predictor of long-term outcome after balloon aortic valvuloplasty28 29 30 and after aortic-valve replacement.31 , 32
In view of the limited hemodynamic improvement and variable reduction in the pressure gradient achieved by balloon aortic valvuloplasty, some investigators have attempted to modify the procedure in order to achieve greater reductions in the pressure gradient and aortic-valve area. These modifications include the use of larger single balloons, double balloons, and deliberate rupture of the balloon to obtain the largest possible valve area.8 , 33 , 34 Although some investigators have reported somewhat larger valve areas with use of these techniques,34 others have not.8 In fact, the use of large balloons may lead to serious complications without affecting long-term outcome.6 , 34 35 36 37 38
Observations on the mechanisms of dilation may explain the limited long-term benefits of valvuloplasty. Despite the presence of fractured calcific nodules, aortic-valve leaflets remain thickened, heavily calcified, and deformed after balloon dilation.35 , 39 In nearly half the cases, simple stretching of the valve leaflets, without morphologic changes in the valve, may result in transient increases in the aortic-valve area, followed by early re-Stenosis.35 , 39 , 40
The multivariate model identified the base-line aortic systolic pressure, the base-line pulmonary-capillary wedge pressure, and the percent reduction in the peak aortic-valve gradient as independent predictors of event-free survival. Although the left ventricular ejection fraction was a strong predictor of event-free survival in the univariate analysis, it was not an independent predictor of event-free survival in the multivariate model. By stratifying patients into clinically important subgroups according to base-line pulmonary-capillary wedge pressure and aortic systolic pressure, we were able to make estimates before valvuloplasty of the probability of event-free survival 6, 12, 18, and 24 months after the procedure (Table 5). Further stratification according to the percent reduction in the peak aortic-valve pressure gradient allowed the prediction of late event-free survival, but these data were available only after valvuloplasty (Table 6). Although these estimates require prospective validation in an independent group of patients, they may provide guidelines for identifying subgroups of patients who are likely to do well after valvuloplasty.
The Role of Balloon Aortic Valvuloplasty and Aortic-Valve Replacement
Although the course of untreated calcific aortic stenosis in elderly patients is poor, balloon aortic valvuloplasty offers substantial palliation of symptoms. In this study, the best long-term results were obtained in patients with a pulmonary-capillary wedge pressure <18 mm Hg and aortic systolic pressure ≥140 mm Hg; these patients had predicted rates of event-free survival of 65 percent at one year and 41 percent at two years. Elderly patients with similar hemodynamic profiles would generally be considered good candidates for aortic-valve replacement, however, with expected perioperative mortality rates of less than 5 percent11 , 12 and one-year, two-year, and five-year actuarial survival rates of 65 to 83 percent, 63 to 81 percent, and 54 to 67 percent, respectively. Although we did not study prospectively a group of age-matched control patients who underwent aortic-valve replacement, the survival data after aortic-valve replacement among the 62 octogenarians studied by Levinson et al.12 (Fig. 1) suggest that patients with good hemodynamic performance have better survival after aortic-valve replacement than after balloon aortic valvuloplasty.
In contrast, patients with a pulmonary-capillary wedge pressure above 25 mm Hg and aortic systolic pressure below 110 mm Hg had predicted rates of event-free survival of 23 percent at one year and 4 percent at two years. In this group, clearly, valvuloplasty offers minimal long-term benefits. Despite the higher perioperative mortality rates of 15 to 33 percent among elderly patients with aortic stenosis and advanced heart failure,11 aortic-valve replacement may offer the best opportunity for long-term survival. In these higher-risk patients, however, it may be reasonable to consider palliative balloon aortic valvuloplasty as a bridge to subsequent early aortic-valve replacement, in the hope of transiently improving left ventricular performance and reducing the risks associated with surgery. Several studies have suggested the value of preoperative valvuloplasty in patients who require urgent noncardiac surgery,41 , 42 but the use of valvuloplasty before aortic-valve replacement has not been studied. Data on early results after valvuloplasty suggest that this approach may have promise for selected patients, but our study did not specifically evaluate this strategy. Although one study found a perioperative mortality rate of 9 percent for 45 patients undergoing aortic-valve replacement 7.8 months after balloon aortic valvuloplasty, the role of preoperative valvuloplasty in lowering the operative risk of aortic-valve replacement was not studied.43
Limitations of the Study
This study is limited, first, by the lack of age-matched patients with aortic stenosis who were treated medically or by aortic-valve replacement. In the absence of a randomized trial, however, there is a substantial body of information available in the literature to allow reasonable comparisons of the long-term outcome of elderly patients treated with balloon aortic valvuloplasty and those treated with aortic-valve replacement. Second, complete hemodynamic or echocardiographic follow-up data on these patients were not available, since the majority of patients were referred from remote geographic locations. Although this lack of data may preclude the accurate estimation of the incidence of re-Stenosis after aortic valvuloplasty, the clinical follow-up reported in this study is 100 percent complete. Finally, this study does not provide direct evidence to support the use of balloon aortic valvuloplasty as a bridge to aortic-valve replacement, but the short-term hemodynamic improvement after valvuloplasty suggests that such a treatment strategy could be reasonable in selected patients.
Conclusion
Balloon aortic valvuloplasty is a short-term palliative procedure for elderly patients with symptomatic aortic-valve stenosis. Although the majority of patients have immediate clinical improvement after successful valvuloplasty, the long-term outcome is limited by re-Stenosis, which occurs in over 50 percent of patients within one to two years. The most important determinants of event-free survival are factors associated with base-line left ventricular function, rather than the extent of improvement in aortic-valve area.
The best long-term results after balloon aortic valvuloplasty were obtained among patients who would have been expected to have excellent long-term results after aortic-valve replacement. Patients with severe left ventricular dysfunction, who are often considered to be poor candidates for aortic-valve replacement, may have only limited long-term clinical improvement after valvuloplasty, a fact that limits the application of the procedure in this high-risk subgroup. Balloon aortic valvuloplasty should be considered for patients who are not candidates for surgery and possibly for patients with severe left ventricular dysfunction as a bridge to subsequent aortic-valve replacement.
Supported in part by a Research Service Award (IF32 HL07987–01A1) to Dr. Kuntz from the National Institutes of Health.
Source Information
From the Charles A. Dana Research Institute and the Harvard—Thorndike Laboratory of the Cardiovascular Division, Beth Israel Hospital (R.E.K., A.D.B., P.C.G., B.M.L., R.G.M., D.J.D., R.D.S.), the Division of Clinical Epidemiology, Beth Israel Hospital and Brigham and Women's Hospital (A.N.A.T., L.G.), the Department of Health Policy and Management, Harvard School of Public Health (A.N.A.T.), and Harvard Medical School, all in Boston. Address reprint requests to Dr. Safian at William Beaumont Hospital, Division of Cardiology, 3601 W. 13 Mile Rd., Royal Oak, MI 48073.
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CrossRef24
(1992) Balloon Aortic Valvuloplasty. New England Journal of Medicine 326:2, 138-139
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